The majority of municipal solid waste (MSW) disposal procedures in the U.S. involve end-dumping of loose material followed by spreading by a dozer and compaction by the dozer or a landfill compactor. The compacted waste is then covered with soil, tarps, greenwaste or other alternative daily cover (ADC) materials. These ADC materials, other than tarps and foam, consume a portion of the available airspace. The MSW is subjected to additional loads of future overlying layers. These loads cause additional compression of the waste. Also, cover soil is often temporarily stockpiled over waste, which compresses the waste. A significant factor contributing to airspace over time is settlement from decomposition of the waste. Waste placement, initial compaction, stockpiling soils above waste, and use of ADCs are evaluated relative to short- and long-term airspace utilization. A proven method developed by the authors and used at three major southern California landfills for predicting settlement, including the contribution of aerobic/anaerobic refuse decomposition, is summarized. The decomposition predictions are based on waste composition and landfill gas (LFG) generation rates. Finally, a clear and easy-to-use method for tracking airspace is discussed, with several recommendations presented for practical application by landfill owners/operators.
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